JPH0261434B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention replaces at least 50 mol% of the titanium in lead titanate with magnesium and tungsten,
The present invention relates to a dielectric material based on lead titanate in which a portion of the magnesium is further substituted with a transition metal, and to the production of said dielectric material. Dielectrics of the above type are important in the manufacture of capacitors, especially multilayer capacitors. Monolithic ceramic multilayer capacitors can have significantly large capacitances with small volumes and high reliability. The starting ceramic material is treated with a binder to create a thin foil. A metal paste is then applied onto such a ceramic foil to form an electrode, and the foil is subsequently stacked with alternating ceramic and metal layers. Since the series of dielectric and electrode layers created in this way is sintered as a single assembly, the electrode materials and sintering conditions must be selected so that the metal layers do not melt or oxidize. . It is known to produce multilayer capacitors in which ceramic materials are densely sintered in air at temperatures above 1300°C. At such sintering temperatures only noble metals with very high melting points, such as palladium or platinum, can be used as electrode metals. Precious metals are extremely expensive, some are not available in abundance, and they also have no relation in price to ceramic materials (as a result of the high degree of mechanization already achieved in multilayer capacitor production) The material costs for the electrodes are particularly important), making it possible to do without expensive palladium or platinum electrodes and to use silver electrodes in their place. Various attempts have been made to produce at significantly lower sintering temperatures. PbTiO ₃ −Pe (Mg _1/2 W _1/2 )
A ceramic dielectric based on the O ₃ system has been awarded a U.S. patent.
Known from specification No. 4063341, it is 950-1000℃
Can be sintered at a temperature of
It has a dielectric constant ε > 1000, which is a useful value. For the production of multilayer capacitors from the ceramic materials described in U.S. Pat. No. 4,063,341, silver should be used as the electrode metal. We have confirmed that this ceramic material cannot be used to produce multilayer capacitors with reproducible quality using silver electrodes. This is because the sintering temperature of the ceramic material is too close to the melting point of silver. However, based on its electrical properties, silver has excellent suitability as an electrode metal and should be supported if possible. The object of the present invention is to reduce the sintering temperature of ceramic materials of the above-mentioned type to well below the melting point of silver and to improve the electrical properties, in particular the dielectric constant ε and the dielectric loss factor tan δ, as well as the resistivity and life test. Subsequent changes thereto are intended to further improve known ceramic materials. This purpose is based on a stoichiometric basic compound with the following composition: Pb(Ti _1-xy Mg _x W _y )O ₃ where 0.25≦x≦0.35 and 0.25≦y≦0.35, on a molar basis of additives. The combination of 5PbO + 1WO ³ is 0.001 to 0.006
This is achieved by adding As a result of the addition of the eutectic (5PbO+ _1WO3 ) with a melting point of 720[deg.]C, sintering temperatures in the range 830-1000[deg.]C, in particular 830-900[deg.]C, can be used and further improved dielectric properties can be achieved. The value of dielectric constant ε is approximately 1500 ~
5400, the value of dielectric loss factor tanδ at 1KHz is between about 1.6-3.1%, and the value of resistivity is 25℃
It is between about 2×10 ¹¹ and 1×10 ¹³ Ωcm. In the present invention, the objective is to satisfy the following formula: Pb(Ti _1-xy Mg _xz Me _z W _y ) O ₃ +0.001~0.006 (5PbO+1WO ₃ ) where 0.288≦x≦0.299 y=0.3 0.001≦z≦0.012 and Me are most advantageously achieved with a dielectric having a composition corresponding to a transition metal. When replacing 0.1-1.2 mol % of magnesium with at least one transition metal Me such as Cr, Mn, Fe or Co, significant improvements in resistivity values are obtained with the already obtained advantages of favorable dielectric properties and low sintering temperatures. It will be done. For example, ceramic materials based on the above composition are
It has a dielectric constant ε value ranging from 2300 to 6100, a dielectric loss factor tan δ value at 1 kHz ranging from 0.3 to 3.1%, and a resistivity value ranging from 8×10 ¹⁰ to 2×10 ¹³ Ωcm at 25°C. Sintering temperature is 830~1000℃, preferably 830~
It is in the range of 900℃. If the process is carried out in such a way that after mixing and grinding the compounds forming the stoichiometric basic compounds, the calcination step is carried out in the range 700-750 °C, and therefore at relatively low temperatures, the evaporation of PbO is This has the advantage of being avoided to a considerable extent. The advantages achieved by the present invention are primarily due to the optimum low sintering temperatures, such that good multilayer capacitors are reproducibly obtained, even when silver is used in pure form as the electrode metal, which is desirable due to its electrical properties. The point is that it is possible to produce ceramic dielectrics that reach the ceramic properties, electrical properties, and dielectric properties of ceramics. Another advantage of the dielectric according to the invention is that the dielectric constant ε exhibits a relatively small temperature dependence.
Deviation from ε value at ambient temperature is -55℃ to +
Although preferably less than ±15% over a temperature range of 125°C is appropriate for practical purposes,
Slightly larger deviations are also suitable for practical purposes. Further advantages of the dielectric of the invention are: By adding the (5PbO+1WO ₃ )-mixture, the sintering temperature can be lowered by 100-150° C. compared to the prior art composition. This reduces lead evaporation and
It is also a decisive advantage in the production of ceramic capacitors, especially multilayer capacitors, since it allows the use of inexpensive silver electrodes with good reproducibility and efficiency, for example in multilayer capacitors. Transition metal ions such as Mn, Cr, Fe and/or
Alternatively, by incorporating Co, the low resistivity value increases especially at 125°C. Only as a result of this do these dielectrics reach insulation values high enough for the application. The incorporation of transition metal ions (in particular Mn and Cr) significantly improves the lifetime properties, so that this material can be used optimally as a dielectric for ceramic capacitors and in particular for multilayer capacitors.
As a result of incorporating Mn, the dielectric loss factor tan δ value can be significantly reduced below 1%. Next, the present invention will be explained in detail by way of examples with reference to the drawings. In the drawings: Figure 1 shows the shrinkage behavior for the dielectric of the invention. FIG. 2 is a graph showing the change in resistivity ρ as a function of time t after a life test of the dielectric, comparing the dielectric of US Pat. No. 4,063,341 with various dielectrics of the present invention. The numbers correspond to the compositions in the table. The shrinkage behavior at the sintering temperature was studied for all samples using a dilatometer furnace to better define the sintering properties. FIG. 1 shows the shrinkage behavior for a dielectric having the following composition: Pb(Ti _0.4 Mg _0.294 Mn _0.006 W _0.3 )O ₃ +0.003(5PbO+1WO ₃ ). At a constant heating rate, the dilatometer furnace used
Once the temperature reaches 1000℃, it is kept at this temperature for 200 minutes and cooled again at the same rate as the heating rate. Parallel to this temperature change T, the shrinkage Δl of various ceramic samples is measured as a function of time t. In Tables 1 to 8 below, the shrinkage onset temperature (T _E ; T _E =580°C for the sample according to Fig. 1) and the temperature at which longitudinal shrinkage reaches 5% (T ₅ %; Fig. 1 T ₅ % = 780℃)
shows. A shrinkage of 5% means that this final density is approximately halfway between the starting density of the untreated ceramic material and the theoretically possible density. The curve in Figure 1 shows that the sample is in a heating cycle.
Already high final density reached at 900℃, 1000℃
shows that no significant contraction occurs anymore in the isothermal phase at . A sintering temperature of 900° C. is therefore sufficient for the dielectric of the invention of the following composition: where 0.288×0.299 y=0.3 0.001z0.012 and Me=transition metal. In Tables 1 to 8 below, the sum of relative shrinkage values ΣS=Δa/a+Δb/b+Δl/l is further plotted in %. Note that a , b and l are the lengths of the ribs of the test sample. To further characterize the sample, the dielectric constant ε value at 25℃, the temperature in degrees Celsius of the highest value of ε, −55℃, −30℃, +10℃, +85℃ from the ε value at 25℃
and the deviation in % of the ε value at +125°C,
and dielectric loss factor in % at 25°C and 1kHz.
Indicates the value of tanδ. Insulation resistance was measured at 25°C and 125°C. In this measurement, a DC voltage of 240 V was applied to a sample with a thickness of 0.5 mm, and the current was measured 1 minute after the voltage was applied. The resistivity values shown in the table are obtained. Life tests were carried out on some compositions which were found to be suitable for practical application in the production of multilayer capacitors at 125°C and a field strength of 4V/dc voltage.
It was carried out at μm=2000V/0.5mm. The time-dependent current flowing through the sample was measured and the resistivity was calculated from this.

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[Table] Explanation of measurement results in Tables 1 to 8 1 Decrease in sintering temperature due to addition of (5PbO+1WO ₃ ). Sample number 1 in Table 1 is a conventional dielectric, and sample numbers 2 to 27 are reference example dielectrics.
A T ₅ % value of 860°C was found from dilatometer measurements;
This composition still exhibits open porosity after sintering at 900° C. for 2 hours and is therefore unsuitable as a capacitor dielectric. A density of 8.25 g/cm ³ was found after sintering at 1000° C., which means that there is still a porosity of 5-6% for a theoretical density of 8.73 g/cm ³ . Sufficient density for a capacitor dielectric is achieved with this, but the optimum value for the dielectric constant ε cannot be achieved with a value for a density of about 8.25 g/ ^cm3 ; these are between 8.4 and 8.5 g/cm3.
This only occurs at densities better than cm ³ (porosity <3%).
Since the optimum density is only reached at sintering temperatures higher than 1000 °C, this composition is suitable for silver electrodes (melting point 960.5 °C).
It is unsuitable as a dielectric material to be sintered together. The following composition: Pb(Ti _1-xy Mg _x W _y ) O ₃ where 0.25≦x≦0.35 0.25≦y≦0.35 The sintering temperature of the basic compound ranges from 0.001 to 0.006 on a molar basis of additives. It can be significantly reduced by adding (5PbO+1WO ₃ ). As is clear from Table 1, the T ₅ % value varies from 860°C for sample No. 1 (composition of the prior art) to No. 2 ~
765℃ for 27 samples (composition according to reference example)
be reduced to. sample number 1 in 2 hours
While it still shows open porosity in a sintering environment of 900°C, the sample with this composition in the reference example sintered at 800°C.
can be densely sintered. As the additive of (5PbO + 1WO ₃ ) increases, the ε value increases from 0.002 to 0.003.
The highest values of 5400 and 5300 are reached with the addition of . 2. Resistivity, dielectric loss, and ε(T) characteristics due to the inclusion of transition metals. The following composition according to the invention: Pb(Ti _1-xy Mg _xz Me _z W _y ) O ₃ + 0.003 (5PbO + 1WO ₃ ) where 0.288x0.299 y = 0.3 0.001z0.012 and Me = basic transition metal Table 2: Influence of the inclusion of transition metals (Cr, Mn, Fe and/or Co) in the compound: The inclusion of Mn substantially improves the dielectric properties of the ceramic material without affecting the good sintering properties. In particular, at 125°C, the resistivity of the sample No. 1 in Table 1 (prior art ceramic material) is
10 Increase by ³ times. The dielectric loss drops below 1% and the ε(T) feature also becomes flatter. Tables 3, 4 and 5: The following composition according to the invention: Pb(Ti _1-xy Mg _xz Me _z W _y ) O ₃ +0.003 (5PbO+1WO ₃ ) where 0.288x0.299 y=0.3 0.001z0.012 and Incorporation of Cr, Fe and/or Co into the basic compound of Me=transition metal also causes an improvement in the dielectric properties with respect to the sample number 1 in Table 1. The dielectric constant ε value increases to 6000 (sample number 70),
The resistivity values are also improved by three orders of magnitude. Table 6 shows the results of mixing a combination of 0.3 mol% Mn and 0.3 mol% Cr. Table 7: Certain basic compounds Pb (Ti _0.4 Mg _0.294 Mn _0.006
W _0.3 ) Various amounts of PbO+WO ₃ were added to O ₃ .
The following conclusions can be drawn from the results in Table 7: The addition may be carried out already before firing, i.e. immediately when the basic substance is weighed (for this purpose, the samples with sample numbers 80 and 81 are replaced by the samples with numbers 33 and 34). ). It is not strictly necessary to add PbO and WO ₃ in the form (5PbO+1WO ₃ ) corresponding to the eutectic composition. However, an overdose of about 1 mol% PbO is essential. Sample with only WO ₃ added (see sample number 82)
exhibits a density of only 8.33 g/cm ³ at a sintering temperature of 900°C. Higher doses of PbO are not very critical; however, an addition of 0.003 (5PbO+ _1WO3 ) is recommended as optimal. An important characteristic of ceramic capacitor materials is their behavior in life tests. This is because the electrical characteristics of a capacitor, especially its resistivity value, are affected by high temperature and high DC voltage electric field strength (4V/
μm) and should be maintained after 1000 hours of loading (for specification X7R).
125℃, 85℃ for specification Z5U). Figure 2 shows the measurement results of the life test at 125°C. The prior art composition (Table 1 sample no. 1) already had a significantly lower resistivity after 1 hour and showed electrical breakdown after 10 hours, whereas the samples with small amounts of Mn or Cr added (sample no. 28,
30) has a resistivity that increases over time, especially above 10 ¹⁴ Ωcm. Samples with a high Mn content (sample no. 36, 38) as well as a sample with a Co content of 0.3 mol % (sample no. 58) show a time-independent resistivity. Very pure quality PbO, as starting material for perowskite basic compounds
MgO, _WO3 , _TiO2 , manganese acetate, cobalt oxalate, _iron oxalate and _Cr2O3 are useful.
Weigh out the basic substances according to the molar amounts shown in the table;
Instead of oxalates or acetates it is also possible in principle to use carbonates or other compounds which can be decomposed at the calcination temperature. 3 basic substances in powder form
Dry milled for an hour, then presintered at a temperature of 700-750°C for 15 hours, and then dry milled again for 1 hour. A prismatic body having dimensions of approximately 6 x 6 x 18 mm is formed from the powder. The prisms were compressed isostatically at a pressure of 4 bar and then at the temperature indicated in the table.
Sintered in _O2 atmosphere for 2 hours. The density of the sintered prism-shaped body is measured by submerging it in distilled water. A rectangular flat plate having dimensions of approximately 5.5 x 5.5 x 0.5 mm is formed from a prismatic body, and a vapor-deposited gold electrode is provided on its surface after lapping. The values of dielectric constant ε (T) and dielectric loss factor tan δ are measured at 1 V at 1 kHz and at temperatures ranging from -55 to +125 °C.
Perform the measurement with a voltage of less than The temperature increase rate was 10°C/min. As a result of the low sintering temperature of the composition in question, it is possible to produce multilayer capacitors with silver electrodes. An example of the production of a multilayer capacitor having a ceramic material of the following composition: Pb(Ti _0.4 Mg _0.294 Mn _0.006 W _0.3 )O ₃ +0.003(5PbO+1WO ₃ ) will now be described. 0.003 (5PbO+ _1WO3 )
The addition of is carried out after calcination of the basic compound material. Very pure quality PbO, TiO ₂ , MgO, as starting materials for perovskite basic compounds
WO ₃ and manganese acetate are helpful. Weigh out these powders according to their molar composition and
Dry milled for 1 hour and then calcined at 700°C for 15 hours. A suitable binder such as polyvinyl alcohol is added to the powder thus obtained and stirred to form a suspension in water. A 50 μm thick foil is formed from this paste, and after drying, silver paste is printed on this to form an electrode layer. To produce the sandwich structure, four foils each with electrode paste and one foil without electrode paste are stacked and compressed. Then slowly add the electrode paste and the bonding agent of the untreated ceramic material to 400% within 24 hours.
Sintering was carried out in air at 850, 900 and 930°C for 2 hours. After sintering, the thickness of the dielectric layer was still 30 μm. Table 8 shows the electrical characteristics of the multilayer capacitor thus manufactured. Comparing these values obtained with multilayer capacitors with those measured with flat plate (disc) capacitors shows good agreement, so much of the data measured with flat plate capacitors (Tables 1-7) can be compared to multilayer capacitors (Table 8). ) can also be moved.

[Brief explanation of the drawing]

FIG. 1 is a graph showing the shrinkage behavior of the dielectric of the present invention, and FIG. 2 is a graph showing the change in resistivity over time of the conventional dielectric and the dielectric of the present invention.

Claims (1)

[Scope of Claims] 1. A dielectric based on lead titanate in which at least 50 mol % of the titanium in the lead titanate is replaced by magnesium and tungsten, wherein the dielectric has a portion of the magnesium replaced by a transition metal. Pb(Ti _1-xy Mg _xz Me _z W _y ) O ₃ +0.001~0.006 (5PbO+1WO ₃ ) where 0.288≦x≦0.299 y=0.3 0.001≦z≦0.012 and Me is a transition metal A dielectric material based on lead titanate, characterized in that it has a composition represented by: 2. The dielectric material according to claim 1, wherein the dielectric material has a composition represented by the formula: Pb(Ti _0.4 Mg _0.294 Me _0.006 W _0.3 )O ₃ +0.003(5PbO+1WO ₃ ). 3 Cr, Mn, Fe or Co as the above transition metal
A dielectric material according to claim 1, characterized in that each of the following is used as one or more transition metals. 4 The above dielectric has the formula: Pb(Ti _0.4 Mg _0.3-z Me _z W _0.3 ) O ₃ + 0.003 (5PbO + 1WO ₃ ) (z = 0.003 to 0.009 in the formula, Me consists of Mn, Cr, Co, and Fe. Claim 1 or 3, characterized in that it has a composition represented by (representing one or more metals selected from the group)
Dielectric material described in section. 5 The above dielectric has a composition represented by the formula: Pb( _{Ti0.4Mg0.294Me0.006W0.3} ) _O3 + _0.001 ~ _0.006 (5PbO+ _1WO3 ) where Me=Cr, Mn, Fe and _/ or Co. A dielectric material according to claim 1, characterized in that: 6 A dielectric based on lead titanate in which at least 50 mol % of the titanium in the lead titanate has been replaced by magnesium and tungsten is provided with a dielectric material based on lead titanate in which part of the magnesium is replaced by a transition metal and has the following formula: Pb(Ti _{1 -xy} Mg _xz Me _z W _y ) O ₃ +0.001 to 0.006 (5PbO + 1WO ₃ ) where 0.288≦x≦0.299 y=0.3 0.001≦z≦0.012 and Me produce a dielectric having a composition represented by a transition metal. In order to do this, the compounds forming the stoichiometric basic compounds are respectively mixed and milled, followed by a calcination step in the range of 700 to 750 °C, after which the product is milled and shaped and then heated to 800 to 750 °C. Densely sintered at temperatures in the range of 1000℃,
A method for producing a dielectric, characterized in that the compounds forming the additive are added to the compounds forming the basic compound before or after calcination. 7. The dielectric according to claim 6, wherein the dielectric has a composition represented by the formula: Pb(Ti _0.4 Mg _0.294 Me _0.006 W _0.3 )O ₃ +0.003(5PbO+1WO ₃ ). Production method. 8 Cr, Mn, Fe or Co as the above transition metal
7. A method for producing a dielectric material according to claim 6, characterized in that each of these transition metals is used as one or more transition metals. 9 The above dielectric has the formula: Pb(Ti _0.4 Mg _0.3-z Me _z W _0.3 ) O ₃ + 0.003 (5PbO + 1WO ₃ ) (z = 0.003 to 0.009 in the formula, Me consists of Mn, Cr, Co, and Fe. Claim 6 or 8, characterized in that it has a composition represented by (representing one or more metals selected from the group)
Method for manufacturing the dielectric described in Section 1. 10 The above dielectric has a composition represented by the formula: Pb( _{Ti0.4Mg0.294Me0.006W0.3} ) _O3 + _0.001 ~ _0.006 (5PbO+ _1WO3 ) where Me=Cr, Mn, Fe and _/ or Co. A method for manufacturing a dielectric according to claim 6.